## CRC-16 Calculation

January 16, 20138 comments Coded in C

This code is the function that calculates a CRC-16 for different purposes. The function requires a POLYNOM from the CRC-16 type.

``````/***** crc16.h *****/
//Tested
#define CRC16_DNP	0x3D65		// DNP, IEC 870, M-BUS, wM-BUS, ...
#define CRC16_CCITT	0x1021		// X.25, V.41, HDLC FCS, Bluetooth, ...

//Other polynoms not tested
#define CRC16_IBM	0x8005		// ModBus, USB, Bisync, CRC-16, CRC-16-ANSI, ...
#define CRC16_T10_DIF	0x8BB7		// SCSI DIF
#define CRC16_DECT	0x0589		// Cordeless Telephones
#define CRC16_ARINC	0xA02B		// ACARS Aplications

#define POLYNOM		CRC16_XXX   // Define the used polynom from one of the aboves

// It calculates the new crc16 with the newByte. Variable crcValue is the actual or initial value (0).
unsigned int crc16(unsigned int crcValue, unsigned char newByte);

/***** crc16.c *****/

#include "crc16.h"

unsigned int crc16(unsigned int crcValue, unsigned char newByte)
{
unsigned char i;

for (i = 0; i < 8; i++) {

if (((crcValue & 0x8000) >> 8) ^ (newByte & 0x80)){
crcValue = (crcValue << 1)  ^ POLYNOM;
}else{
crcValue = (crcValue << 1);
}

newByte <<= 1;
}

return crcValue;
}

/***** EXAMPLE *****/

unsigned int exampleOfUseCRC16 (unsigned char *Data, usigned char len){

unsigned int crc;
unsigned char aux = 0;

crc = 0x0000; //Initialization of crc to 0x0000 for DNP
//crc = 0xFFFF; //Initialization of crc to 0xFFFF for CCITT

while (aux < len){
crc = crc16(crc,Data[aux]);
aux++;
}

return (~crc); //The crc value for DNP it is obtained by NOT operation

//return crc; //The crc value for CCITT
}``````